Any battle can be made more interesting by adding environmental effects. You should try to introduce such features after one or two sessions to grow familiar with the combat rules before experimenting with them!
Here are some examples of environmental effects; the damage they deal should be based on the table on page 93.
This effect grants all creatures a Resistance or Vulnerability to a specific type of damage (such as a cursed cathedral granting everyone Resistance to light damage, or ocean water granting Resistance to fire but Vulnerability to bolt).
This effects adds one or more elements of increasing danger to the scene; perhaps the site of the battle is cursed and causes a new penalty at the end of each round (such as MP loss, a status effect, or direct HP loss). This puts a timer on the battle and forces the heroes to take risks in order to defeat the enemy quickly.
A natural danger or a mechanical contraption might deal damage to some creatures at the end of each round, or to any character that performs a specific action. Typical examples are poisonous fogs, lightning storms, or magical anomalies.
The battlefield might react to specific actions, dealing damage to all participants or to randomly selected characters. For instance, explosive barrels might detonate whenever a fire-based spell is cast or a fire-based attack is performed.
When you introduce an environmental effect, you should allow Player Characters to find ways to disable it or turn its effects against their adversaries. This will normally require filling a Clock through the Objective action.